One type of toy building unit that has been known for many years is the common wooden toy blocks. Historically, such building units have come in a variety of shapes, sizes and colors. One of the most common types is the small wooden block or cube, approximately 11/2 inches in each dimension. Such wooden blocks have commonly had indicia such as letters cut into the surface. Most children at one time or another have stacked these blocks to form an outline of a wall or building. The wooden blocks have generally not been secured together and therefore any construction is of a very temporary nature. The primary play value in such blocks is in the stacking or assembling of the blocks rather than use of the structure subsequent to stacking.
Another general type of building unit is illustrated by the Lego.TM. blocks such as is shown in U.S. Pat. Nos. 3,005,282 and 3,597,875. The Lego blocks are small units which have a plurality of projections on one surface which coact with a pocket in the surface of the adjacent block. Again, the play value lies primarily in the assembling of many, many blocks into a wall construction or a building construction. The attention span of the child may be expended by the time the blocks are assembled into a building.
A further type of building block is illustrated in U.S. Pat. No. 3,076,286 in which a plurality of blocks are locked together by a dove tail insert which slides into a slot in the adjacent block. The dove tail may be an integral part of the block itself or may be a separate element which is inserted into cooperating slots in adjacent blocks.